Antifoggants and stabilizers for photographic silver halide emulsions



nited States Patent AND STABHJZERS FOR PHOTO- V GRAPHIC SILVER HALIDE EMULSIQNS Fritz Der'scli and Millet R. De Angelus, Binghamton, lI.Y., assignors to General Aniline & Film Corporatron, New York, N.Y., a corporation of Delaware No Drawing. Filed Mar. 13, 1958, Ser. No. 721,100 6 Claims. (Cl. 96-109 The present invention relates to the use of antifogging and stabilizing agents for photographic silver halide emulsions and, more particularly, to the use for such purposes of carboxyalkyl-ethyl-pyridyl or -quinolyl thioethers in whlch the ethyl thioether group is in the 2- or 4-position of the pyridine or quinoline ring, and the salts and esters of said thioethers. v I It is known that light-sensitive emulsions such as photographic silver halide emulsions have a tendency to fog. This fog may be caused in a number of ways, as, for example, by excessive ripening of the emulsion, during storage of the film or paper particularly at elevated temperatures and humidity, or by prolonged development of the exposed emulsion.

A great number of antifoggants and stabilizers have been described in the literature as being effective in preventing an increase in fog to thus stabilize or control the keeping qualities of light-sensitive silver halide emulsions. Among such compounds maybe mentioned benzthiazole, benzimidazole and their Z-mercapto derivatives. Although these compounds have the ability of reducing fog tendencies to thereby improve the stability of the emulsion, they are deficient in that they lower the sensitivity of the emulsion and in some cases reduce its opticalor dye-sensitization. 'We have now found that carboxyalkyl-ethyl-Z or 4- pyridyl or -quinolyl thioethers, their salts and esters are not only excellent stabilizers or antifogging agents for silver halide emulsions but, in addition, they have the happy faculty of performing this function without lowering the sensitivity of the emulsion with which they are associated or without reducing the sensitivity of the emulsion to light of longer wave length attributable to the presence of sensitizing dyes.

The use of such compounds to inhibit fog and to stabilize silver halide emulsions either by locating the same in the emulsion or in layers adjacent thereto or in proc- 'essing baths for the emulsion constitutes the purposes and objects of the present invention.

'- 1 Compounds the use of which is contemplated herein may be represented by the following formulae:

in whic h the side chain is located in the 2- or 4-position of thepyridine or quinoline ring; n is a whole number of from 1 to 3; and R is hydrogen, alkyl, such as methyl, .ethyLpropyl, butyl, amyl and the like; hydroxyalkyl, i.e., hydroxymethyl, hydroxyethyl and the like; carboxyalkyl, i.e., carboxymethyl, carboxyethyl and the like; aryl such 2 as phenyl, tolyl, naphthyl, carboxyphenyl, sulfophenyl and the like; aralkyl such as benzyl or a cation such as hydrogen, sodium, potassium, silver, ammonium or the like.

Examples of compounds within the ambit of such formulae which we have found to be efiective are:

(1) oc-Z-PYIldYl-CthYl thio acetic acid and its potassium,

. -sodium, silver and ammonium salts (2) a-4-pyridyl-ethyl thio acetic acid and its methyl,

- benzyl and phenyl esters (3) fi-(m-2-pyridyl-ethyl thio) propionic acid and its sodium and ammonium salts (4) 13-(a-4-pyridyl-ethyl thio) propionic acid (5) 'y-(a-2-pyridyl-ethyl thio) butyric acid and its butyl ester.

(6) 'y-(a-4 pyridyl-ethyl thio) butyric acid (7) a-2-quinolyl-ethyl thio acetic acid and its methyl,

butyl and benzyl esters (8) a-4 -quinolyl-ethyl thio acetic acid and its sodium and potassium salts (9) fi-(a-2-quinolyl-ethyl thio) propionic acid (10) [i-(a-4-quinolyl-ethyl thio) propionic acid (11) -(a-2-pyridyl-ethyl thio) butyric acid (12) -(a-4-quinolyl-ethyl thio) butyric acid The above compounds may be prepared by the method described in U.S.P. 2,810,724 whileselecting the desired vinyl pyridine or vinyl quinoline and the desired mercapto lower aliphatic acid. In general, this method envisages the addition of a mol equivalent of the mercapto lower aliphatic acid to the selected vinyl pyridine or 01' as coating finals.

quinoline in the presence of a polymerization inhibitor such as, for instance, an anti-oxidant like hydroquinone. Thereaction takes place with evolution of heat and the formation of a crystalline product. If desired, the reaction mixture may be heated to low temperatures such as 4060 C. to complete the reaction. After cooling, the reaction product is treated with ether or ethanol and collected by filtration. The solid product may be purified with charcoal and recrystallized from ethanol.

7 The free acid produced by this method may be converted to its salt by reacting the same with a water soluble salt containing the desired cation such as potassium carbonate, sodium carbonate, ammonium carbonate, silver nitrate or the like.

The esters of the free acids are prepared in the conventional manner by refluxing the same with the selected alcohol or phenol in the presence of hydrochloric acid.

Beneficial effects and fog reduction are obtained when solutions of the aforementioned compounds are incorporated in the silver halide emulsions as ripening finals Ripening finals are added during the ripening or the sensitivity increasing stage of the emulsion making process. Such additions may be made before, during or after the decomposition of the soluble silver salt such as silver nitrate by means of soluble halides such as potassium bromide in the presence of a colloidal carrier such as gelatin, PVA, solubilized casein or albumin.

Coating finals are added to the emulsion just prior to coating on a suitablesupport such as glass, paper or film at a time when the emulsion has nearly obtained its maximum sensitivity.

When used as ripening finals, our antifoggants or stabilizers are best employed in a concentration of 1 to milligrams per .6 mol of silver halide and when used as coating finals in a concentration of 10 to 300 milligrams per .6 mol of silver halide. The concentration depends very much on the type of emulsion which is used, and it is advisable to determine the optimum concentration from case to case. In some instances, it is advantageous to apply this group of antifoggants and 3 stabilizers in adjacent layers, e.g., in a separate undercoating layer or in the anti-abrasion gelatin surface. In other cases, it is desirable to apply them in one or all processing baths or in preand post-baths.

The aforesaid antifoggants and stabilizers may be employed in connection with any type of photographic emulsion, e.g., non-sensitized, orthochromatic, panchromatic, X-ray emulsions, paper emulsions, color emulsions or the like. They may be used in combination with other known antifoggants and stabilizers, reductionand metaland noble metal sensitizers or in combination with hydroxypolyethenoxy derivatives, i.e., those obtained by reacting ethylene oxide with an alcohol, phenol, amine or the like. (See U.S.P. 1,970,578.)

The invention is illustrated by the following examples but it is to be understood that the invention is not to be restricted thereto.

Example I A silver halide emulsion in gelatin containing 2% silver iodide and 98% silver bromide Was prepared in a conventional manner and brought up to its maximum light sensitivity. It was then readied for coating, finals were added such as sensitizing dyes and hardening agents. A 1% solution of a-4-pyridyl-ethyl thio acetic acid was added to the emulsion as an antifoggant and stabilizer. The emulsion samples contained about .6 mol of silver halide. The so-prepared emulsion samples were coated on a suitable cellulose ester base and dried. Samples of these film coatings were then exposed in a Type IIB Sensitometer and developed in a developer of the following composition:

Grams Metol 1.5 Sodium sulfite, anhydrous Sodium bisulfite 1 Hydroquinone 3 Sodium carbonate, monohydrated 6 Potassium bromide .8

Water to make 1 liter.

Quantity of Com Relative Fog at 12 Oven Fog at 6 pound Added Speed Develop- Development ment The antifoggant has the following formula:

C Hi

Example 11 The procedure was the same as in Example I excepting that the a-4 pyridyl-ethyl thio acetic acid was replaced by an equivalent quantity of a-2-pyridyl-ethyl thio acetic acid. The results were similar-to those obtained in Example I.

The antifoggant of this example was prepared in the same way as that of Example I excepting that 2-vinyl pyridine was used in lieu of 4-vinyl pyridine. The antifoggant has the following formula:

H( 3SCHr-COOH II-Ia Example III The procedure was the same as in Example I excepting that there was used an equivalent quantity of p-(a-4- pyridyl-ethyl thio) propionic acid.

This compound was prepared according to the example appearing in U.S.P. 2,810,724.

Example IV The procedure was the same as in Example I excepting that there was used as the antifoggant 'y-(a-4pyridylethyl thio) butyric acid. The results paralleled those of Example I.

The antifoggant was prepared by the method of U.S.P. 2,810,724 but while using -mercapto butyric acid in place of B-mercapto propionic acid.

Example V The procedure was the same as in Example I excepting that there was used as the antifoggant fi-(a-4-quinolylethyl thio) propionic acid.

This antifoggant was prepared by the method of U.S.P. 2,810,724 but while using 4-vinyl quinoline in place of 4-vinyl pyridine.

Example VI An exposed sample of a photographic film was developed for 12 minutes at 65 C. in a standard metolhydroquinone developer. Another exposed sample was similarly developed in the same developing solution except that milligrams of the compound of Example! per liter of developer were added. Sensitometn'c strips developed in the standard developer (control) showed a fog of .30 whereas those strips which were developed in the developer containing the antifoggant had a fog of .20.

Example VII The procedure was the same as in Example VI excepting that there was used as the antifoggant 'y-(a-2- quinolyl-ethyl thio) butyric acid. The results were similar to those obtained in Example VI.

Various modifications of the invention will occur to persons skilled in the art. For example, it is evident that any of the antifoggants listed may be used in lieu of those of the examples. We, therefore, do not intend to be limited in the patent granted except as necessitated by the appended claims.

We claim:

1. A' light-sensitive photographic material comprising a base and a light-sensitive silver halide emulsion layer, said light-sensitive material containing as an antifoggant a compound selected from the class consisting of those of the following formulae:

N wherein n is a Whole number of from 1 to 3; R is selected from the class consisting of alkyl, aryl, ar'alkyl and a. cation, and the sulfur-containing substituent group on the designated nitrogenous heterocyclic ring is in a position selected from the class consisting of the 2- and 4- position of such ring.

5. The process of minimizing and preventing fog in 10 light-sensitive silver halide material, comprising a base having a light-sensitive silver halide emulsion thereon, which comprises exposing said emulsion to light and developing the same in the presence of an antifoggant selected from the class consisting of those of the following formulae:

and

(17H: g-S(CHa)nCOOR wherein n is a whole number of from 1 to 3; R is selected from the class consisting of alkyl, aryl, aralkyl and a cation, and the sulfur-containing substituent group on the designated nitrogenous heterocyclic ring is in a position selected from the class consisting of the 2 and 4- position of such ring.

6. The process as defined in claim 5 wherein the antifoggant is a-4-pyridyl-ethyl thio acetic acid.

References Cited in the file of this patent UNITED STATES PATENTS Mathies et a1 Dec. 31, 1929 Murray et a1. Feb. 23, 1958 

1. A LIGHT-SENSITIVE PHOTOGRAPHIC MATERIAL COMPRISING A BASE AND A LIGHT-SENSITIVE SILVER HALIDE EMULSION LAYER, SAID LIGHT-SENSITIVE MATERIAL CONTAINING AS AN ANTIFOGGANT A COMPOUND SELECTED FROM THE CLASS CONSISTING OF THOSE OF THE FOLLOWING FORMULAE: 